1. Field of the Invention
This invention relates to the art of adjusting diesel engine fuel pump racks to match the governor's power piston gage gap. More particularly, the invention relates to an improved power piston screw jack which is used to raise the power piston sufficiently to clamp the gap gage firmly and then hold it in its clamped position during the adjustment.
2. Description of the Prior Art
In the prior practical art, multi-cylinder diesel engines, such as those having 8, 12 and 16 cylinders, all include: (1) an engine speed control governor having, internally or externally, a vertically movable power piston characterized by a gage gap in the vertical axis of the piston and by a lug integrally secured to project downwardly or depend from the piston; (2) a fuel pump for each engine cylinder, each pump having its own adjustable fuel rack; (3) a pair of long right and left horizontal fuel rack shafts, one for each side of the engine, each rack shaft extending longitudinally along its side of the engine in a vertical plane behind and in a horizontal plane spaced below the corresponding right and left series of air boxes more or less on the level of the right return air manifold; (4) a pair of right and left fuel rack linkage systems, each rack linkage system providing a series of identical trains of mechanism, one train for each fuel rack, each train connecting its fuel rack to the corresponding rack shaft; (5) a cross-over linkage connecting the right rack shaft with the left rack shaft so that when the right rack shaft is operated, the left rack shaft will be simultaneously operated; and (6) a terminal linkage system interconnecting the right rack shaft with the depending lug of the vertically movable power piston, and being characterized by a shaft-mounted overspeed link which, as the fuel feed increases, moves angularly, say upward, about the axis of its shaft and which, as it moves upwardly, raises the power piston accordingly.
When the engine is at top speed, the gage gap should equal a known or predetermined value. For the sake of clarity, we assume hereinafter that this gap equals 0.344 inches. All fuel pump racks must be adjusted to a setting which matches the 0.344 inch gage gap. In effecting this match, the power piston and the outer end of said overspeed link, which are interconnected, must be jacked up to a position simulating or corresponding to the top speed of the engine.
For jacking purposes, one conventional practice comprises: (1) place an 0.344 inch metal gage between the bottom of the governor casing and the top of the vertically-movable power piston; (2) provide a rigidly mounted base platform spaced below the outer end of the overspeed link; and (3) place a vertical screw jack upright upon the base platform and adjust its screw (a) to lengthen or extend the jack vertically into rising engagement with the bottom of the outer end of the overspeed linkage and (b) for further rising movement during which it causes the angularly moving overspeed linkage to move the power piston upwardly along its vertical center axis until the 0.344 inch gage is firmly compressed upwardly against the governor casing by the top of the power piston.
When the gap gage is firmly compressed or clamped, each fuel pump rack may then be separately adjusted to its correct millimeter setting.
After each rack has been individually adjusted and before the engine is restarted, the screw jack should be returned to its normal inoperative position and removed. Occasionally, a workman may start the diesel engine with the screw jack in its gage clamping position. When this is done, the engine will take off with a continuously rising speed. Before the adjusting screw of the jack can be sufficiently unscrewed, the engine may be seriously damaged or completely wrecked.